hwmon: (pmbus/max8688) Accept negative page register values

A negative page register value means that no page needs to be
selected. This is used by status register evaluations and needs
to be accepted.

Fixes: da8e48ab ("hwmon: (pmbus) Always call _pmbus_read_byte in core driver")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/max8688.c

@@ -45,7 +45,7 @@ static int max8688_read_word_data(struct i2c_client *client, int page, int reg)
 {
 	int ret;
 
-	if (page)
+	if (page > 0)
 		return -ENXIO;
 
 	switch (reg) {